This invention relates to a vehicle traction control system and, more particularly to such a system which provides for such control by control of both the brakes of the driven wheels and engine torque output.
It is a common experience with automotive vehicles for excessive wheel spin to occur during vehicle acceleration when the operator initiated engine torque delivered to the vehicle driven wheels are such that the frictional forces between the tire and the road surface are overcome. While a small amount of spin between the tire and road surface is necessary in order to achieve a driving force, excessive spin results in the reduction of effective driving force and in the deterioration in the lateral stability of the vehicle.
It is known that excessive spinning of vehicle driven wheels can be prevented by applying the brakes of a spinning wheel so as to limit the slip between the wheel and the road surface at a value that will achieve a maximum transfer of driving force from the driven wheels to the road surface. An advantage of limiting wheel slip by application of the brakes of the spinning wheel is that excessive acceleration spin can be quickly brought under control. However, if the brake pressure is controlled in the same manner for all accelerating conditions of a vehicle, harshness of vehicle operation may result. For example, a rapid application of brake pressure to capture an excessive spin condition that provides acceptable performance under conditions of high engine torque demand may result in harshness of vehicle operation under conditions of low engine torque demand.